Which server is it? If it's only one server giving you trouble, you might be banned from it. Or it might auto kick for high ping or something. Where do you live and what server are you trying to enter?
Also, are you running it as an administrator with Vista? You have to do that, because PunkBuster checks deep within your computer for the stuff it looks for, and Vista doesn't like that if you aren't running as an admin.
Another thing is the server might be running a map you don't have, but I don't know if you would be able to get in as far as you say you can get in, if that's the case.
The 16 maps included in a standard FH 2.15 installation are: Bardia, Invasion of Crete, Sidi Rezegh, Siege of Giarabub, Siege of Tobruk, The Battle for Sfakia, Alam Halfa, El Alamein, Fall of Tobruk, Gazala, Mersa Matruh, Operation Aberdeen, Operation Hyacinth, Operation Supercharge, Mareth Line, and Tunis. Any other maps you have to get from a Map Pack, or direct from whoever made it (such as the Tournament-specific maps). I'm not sure if that's the problem or not.
Wait, were you one of the guys who tried to load into the World at War Server last Saturday? We were doing a special practice in preparation for the next campaign. The version of The Battle of Salerno we were using hasn't been released to the public. That might be the problem. A couple of the WaW servers should be password-protected, but aren't and they are running non-standard maps. One of the Forgotten Honor servers is (apparently, I'm not part of that tourney) also running non-standard maps, but is not password-protected. There is also another server (Olde German Power) that is running a non-standard map and isn't password protected.
The more I think about, the more it seems like you just don't have the right map. If you post what server you were trying to get into and what map they were playing (as well as whatever other info you think might be helpful), it would help to narrow down the problem.